I. Field of the Invention
This invention relates to adsorbents used for the removal of acid components, e.g. acids and acidic materials, from gases and liquids. Most particularly, the invention relates to activated alumina-based adsorbents of this kind and to processes for the preparation of such adsorbents.
II. Description of the Prior Art
There are many industrial processes in which it is desirable to remove traces of acids and acidic materials from gases or liquids in order to avoid damage to equipment, environmental pollution or problems during recycling of a product stream to an earlier reaction.
For example, small quantities (e.g. several ppm) of HCl are produced during the catalytic reforming of low octane hydrocarbon fuels into high octane products. The reaction produces hydrogen gas which is recycled to the reforming reaction, but traces of the HCl originating from chlorides which are injected into the feed stream to regenerate the catalyst must first be removed to avoid interference with the operation and corrosion of the equipment.
Activated alumina has been used in the past as a scavenger for the removal of the small quantities of HCl from the hydrogen gas streams, but the efficiency of acid removal of this material is rather limited and there is a need for more effective and long-lived acid absorbers.
U.S. Pat. No. 4,639,259 which issued on Jan. 27, 1987 to Michael J. Pearson describes a more effective acid scavenger comprising an alkaline earth metal-promoted alumina-containing material. The preferred alkaline earth metals are said to be calcium and magnesium added to activated alumina or bauxite in a conventional manner, such as impregnation, followed if desired by shaping, e.g. nodulization or extrusion and subsequent thermal activation. While the resulting scavenger material may be more effective than activated alumina itself, it is believed that there is a need for further improvement, particularly in the effective life of the acid adsorbent, i.e. the amount of acid it can absorb before replacement or reactivation is required.
U.S. Pat. No. 4,762,537 to Fleming et. al. issued on Aug. 9, 1988 discloses an acid adsorbent formed by agglomerating alumina particles in the presence of water and Y zeolite particles. It is stated that the zeolite makes up for the rather poor acid adsorption of alumina at low concentrations. However, zeolites are rather expensive materials and the resulting adsorbents are thus not likely to gain wide acceptance for commercial operations.
Accordingly, there is a need for relatively inexpensive but nevertheless effective adsorbents for acids suitable for use in the processes mentioned above and for other procedures in which traces of acid must be removed from gases or liquids.